Failover is one of the most highly desired functions in a modern communications network. The failover function automatically detects a communications link or a communications network node failure experienced in a communications network, and switches the affected traffic onto alternate paths away from the failed communications link or failed communications network node. The process of switching the affected traffic from one path to another must happen rapidly enough so as to protect high-priority, high bandwidth, or real-time flows from experiencing disruptions.
Existing schemes that provide failover rely on either the Layer 2 spanning tree protocol described in IEEE 802.1d protocol, which is incorporated herein by reference, and/or Layer-3 routing control protocols such as, but not limited to: the Border Gateway Protocol (BGP), Cisco's Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), all of which are incorporated herein by reference. Employing the Layer-2 scheme, the spanning tree protocol dynamically modifies an acyclic set of edges that spans the network whenever a communication link and/or a communications network node fail. At Layer-3, routing control protocols compute alternative routes whenever the communications network topology changes, including due communications link or communications network node failures.
However, neither one of the above two schemes provides failover that is sufficiently rapid so as to prevent service disruptions for high-priority, high bandwidth, or real-time services. The typical convergence time of the spanning tree protocol, the time taken to compute a new spanning tree, is around 45 seconds. Recently, a rapid spanning tree protocol IEEE 802.1w, which is incorporated herein by reference, has been proposed for reducing the expected convergence time to 5 seconds for a very small spanning tree/communications network. Accordingly, the convergence time for a large spanning tree/communications network is still in the tens of seconds, measured at 5 additional seconds for every extra hop. Layer-3 route re-computations are equally slow.
The related art includes co-pending commonly assigned U.S. patent application Ser. No. 10/284,856 entitled “High Availability Ethernet Backplane Architecture” filed by Wang et al. on Oct. 31, 2002, and co-pending and commonly assigned U.S. patent application Ser. No. 10/326,352 entitled “Apparatus for Link Failure Detection on High Availability Ethernet Backplane” filed by Wang et al. on Dec. 20, 2002 which is a continuation-in-part of U.S. patent application Ser. No. 10/284,856; both of which are incorporated herein by reference. These related co-pending and commonly assigned U.S. patent applications describe communications-network-node-based failover functionality wherein redundant node boards and redundant switch fabric boards routinely perform attached communications link integrity checks such that each can independently initiate failover to working ports when a link failure is detected.
While the related art describes desirable inventive and effective hop-by-hop failover communications-network-node-based functionality, there is a need to provide rapid end-to-end failover functionality.